I just ordered and installed the JBD chip last week set at default settings.
Yes the engine feels a little stronger than before. The notice that came with it says "off road use only" so you may want to take it of for service and smog check if there is (do they smog diesels now?).
Not sure about the mileage yet, I only drove a quarter tank since I installed it. Do others see better, same or worse mileage ?

Since the tune only affects the boost peak, mileage should be nearly identical except for those seconds you hold it full throttle.

For some reason, my mileage increased on my 335i with the tune (maybe the engine broke in?).